Substrates used in making devices such as flat panel displays, active electronic devices, photovoltaic devices, and biological arrays are typically required to have surfaces that are substantially free of defects and with flatness to within a few microns. Therefore, it is important that these surfaces can be inspected for defects and flatness relatively easily. Phase measurement interferometry (PMI) is an example of an optical interferometry technique for measuring surface topography. PMI generally involves creating interference patterns through interaction of light beams with the surface of an object and detecting the interference patterns, where the detected interference patterns are used to reconstruct the surface topography. PMI generally relies on area scan cameras to detect interference patterns. However, area-based PMI has limited use in high-speed inspection of large substrates, such as those used in flat panel displays. One challenge is that area scan cameras have a limited field-of-view. Another challenge is that area scan cameras are difficult to scale. In general, the larger the area scan camera, the more complex the area scan camera, resulting in long scanning time and high cost.